5:14 a.m.
I am trying to write a simple app which connects a channel obtained
from virDomainOpenChannel() to stdin/stdout (based in part on the
snippet at [1]). However, it seems like the data received back from
the stream is delayed by one iteration. It would be hard to explain
this by simply showing the output, so here's a timeline instead:
1. start the program on the host
2. write "msg from host<Enter>"
3. socat on the guest sees this right away
4. from the guest's socat, write "msg from guest<Enter>"
5. the reply does not show up on the host until AFTER you press
<Enter> (which of course also sends a newline to the guest)
6. this 'one line delay' occurs throughout the conversation,
receiving guest replies to things sent two <Enter>s ago
Doing socat on both sides work as expected. Also, using a blocked
stream and a thread for sending and another for receiving works
as well. It would be nice however if I could get rid of the threads
in favour of callbacks. Not sure if I'm missing something obvious.
Thanks,
Jonathan
[1] https://www.redhat.com/archives/libvir-list/2012-December/msg01084.html
---
#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <libvirt/libvirt.h>
#include <fcntl.h>
#define CONNECT_URI "qemu:///system"
#define DOMAIN "TestVM"
#define CHANNEL "channel.0"
#define BUF_SIZE 80
int stream_active = 1;
void
stdin_to_stream(int watch, int fd, int events, void *opaque)
{
virStreamPtr stream = *((virStreamPtr*)(opaque));
if (events & VIR_EVENT_HANDLE_READABLE) {
char buf[1024];
int bytes_read = read(fd, buf, sizeof(buf));
if (bytes_read > 0)
virStreamSend(stream, buf, bytes_read);
}
if (events & (VIR_EVENT_HANDLE_ERROR|VIR_EVENT_HANDLE_HANGUP)) {
stream_active = 0;
}
return;
}
void
stream_to_stdout(virStreamPtr stream, int events, void *opaque)
{
if (events & VIR_EVENT_HANDLE_READABLE) {
char buf[1024];
int bytes_read = virStreamRecv(stream, buf, sizeof(buf));
if (bytes_read > 0) {
fwrite(buf, bytes_read, 1, stdout);
fflush(stdout);
}
}
if (events & (VIR_EVENT_HANDLE_ERROR|VIR_EVENT_HANDLE_HANGUP)) {
stream_active = 0;
}
return;
}
int main(int argc, char *argv[])
{
virConnectPtr conn;
virDomainPtr dom;
virStreamPtr st;
int bytes_read;
char buf[BUF_SIZE];
if ((conn = virConnectOpen(CONNECT_URI)) == NULL)
errx(1, "virConnectOpen");
if ((dom = virDomainLookupByName(conn, DOMAIN)) == NULL)
errx(1, "virDomainLookupByName");
if ((st = virStreamNew(conn, VIR_STREAM_NONBLOCK)) == NULL)
errx(1, "virStreamNew");
if (virDomainOpenChannel(dom, CHANNEL, st, 0) == -1)
errx(1, "virDomainOpenChannel");
if (virEventRegisterDefaultImpl() != 0)
errx(1, "virEventRegisterDefaultImpl");
if (virStreamEventAddCallback(st, 1|4|8, stream_to_stdout, NULL, NULL) != 0)
errx(1, "virStreamEventAddCallback");
int flags = fcntl(fileno(stdin), F_GETFL) | O_NONBLOCK;
fcntl(fileno(stdin), F_SETFL, flags);
if (virEventAddHandle(fileno(stdin), 1|4|8, stdin_to_stream, &st, NULL) < 0)
errx(1, "virEventAddHandle");
while (stream_active) {
if (virEventRunDefaultImpl() != 0) {
errx(1, "virEventRunDefaultImpl");
break;
}
}
if (virStreamFinish(st) < 0)
errx(1, "virStreamFinish");
if (virStreamFree(st) < 0)
errx(1, "virStreamFree");
return 0;
}